As the amount of data transmission continues to increase in recent years, the need for mobile communication systems with higher spectra efficiency also increases, and investigations into one-cell reuse cellular systems in which the same frequency band is used for all cells continue to advance. A one-cell reuse cellular system using the Orthogonal Frequency Division Multiple Access (OFDMA) method is adopted as a downlink transmission method regarding an Evolved Universal Terrestrial Radio Access (E-UTRA) system, which is becoming a standard through such organizations as the 3rd Generation Partnership Project (3GPP). Also, the non-contiguous/contiguous Discrete Fourier Transform Spread OFDM (DFT-S-OFDM) method, which is a discrete Fourier transform OFDM method that supports non-contiguous frequencies and contiguous frequencies, is being investigated as a valid candidate for an uplink transmission method.
The OFDMA method, which is the downlink transmission method, is a method using OFDM signals, which have superior resistance to multi-path fading, in which a user accesses in units of resource blocks (RB) divided by time or frequency. However, as the OFDMA method has high Peak-to-Average Power Ratio) PAPR properties, this is not applicable as an uplink transmission method, which has severe transmission power restrictions.
Conversely, the DFT-S-OFDM method can maintain excellent PAPR properties regarding multi-carrier methods such as OFDM by using signals spread by DFT in contiguous frequencies (RB), which ensures a wide coverage. Also, the DFT-S-OFDM method flexibly uses frequencies by using non-contiguous frequencies, and at the same time, can suppress degradation of PAPR properties to a certain extent. Also, it is being investigated if the switching between non-contiguous and contiguous frequencies in the non-contiguous/contiguous DFT-S-OFDM can be performed on the basis of the transmission power (refer to PTL 1 for example, hereafter referred to as a hybrid method). By using this hybrid method, cell coverage is maintained as a method using only contiguous DFT-S-OFDM, and at the same time, throughput of terminals within the cell can be improved, which also improves the throughput of the overall cell.
Conversely, a frequency clipping technology is also being investigated in which a portional frequency spectra regarding the DFT-S-OFDM method is not transmitted (hereafter, referred to as clipped DFT-S-OFDM) (for example, PTL 2).
FIG. 20 illustrates an example configuration of a transmitting device 1000 when using clipped DFT-S-OFDM for the uplink transmission. As in FIG. 20, an encoding unit 1001 performs error correction encoding on a transmission data D100. Next, a modulating unit 1002 performs modulation on the transmission data. A Discrete Fourier Transform (DFT) unit 1003 conducts a discrete Fourier transformation to convert the modulated symbols into frequency domain signals. Here, a symbol number NDFT0 (DFT size) to be converted one time is determined by a clipping amount and the bandwidth allocated to the transmitting device 1000 by a clipping control unit 1004.
Next, a clipping unit 1005 clips a portion of the output from the DFT unit 1003 based on the clipping information output from the clipping control unit 1004, and outputs the remaining signal to a mapping unit 1006. Here, clipping represents the amount of signal removed, and a clipping ratio Rclip is defined as Rclip=1−[output sub-carrier number of the clipping unit 1005 (divided frequency point number)]/NDFT0. However, when the clipping ratio is zero, the signal output from the clipping unit 1005 represents the normal DFT-S-OFDM signal. The components of the clipping signal may be previously determined positional components, or may be advertised by a control station such as a base station at every transmission in the same way as mapping information, which is described next. In the same way, the clipping ratio may be a predetermined ratio, or may be advertised from a control station such as a base station at every transmission.
The mapping unit 1006 allocates the signal output from the clipping unit 1005 into a sub-carrier (resource block) used in transmission. The mapping unit 1006 performs this allocation based on mapping information, and inserts a zero into a sub-carrier within this allocation that cannot be used in transmission. Further, known information between the transmitting device and the receiving device is used for this mapping information, and with regard to the obtaining method at the transmitting device mapping information, for example, mapping information determined by the receiving device that has been received as control information is used.
The methods to allocate the transmission signal into the sub-carrier used in transmission include a method to allocate the sub-carrier contiguously, and a method to allocate non-contiguously. When using a contiguous sub-carrier with a clipping ratio of zero, the generated signal is equivalent to a single carrier signal.
The transmission signal allocated into the sub-carrier to be used in transmission is input into an Inverse DFT (IDFT) unit 1007. The IDFT unit converts frequency domain signals into time domain signals by performing an inverse Fourier transformation on the input transmission signal. A reference signal generating unit 1008 generates a reference signal (also referred to as an RS signal or a pilot signal) used for estimating a propagation path at the receiving device. A reference signal multiplexor unit 1009 multiplexes the reference signal generated by the reference signal generating unit 1008 with the data signal output from the IDFT unit 1007, and outputs this to a transmission processing device 1010.
The transmission processing device 1010 inserts a Cyclic Prefix (CP), which is also referred to as a Guard Interval (GI), into the input transmission signal, conducts a Digital to Analog (D/A) conversion and upconverts to a carrier frequency band, and outputs the signal to the receiving device via a transmission antenna 1011.
FIG. 21 illustrates an example configuration of a clipped DFT-S-OFDM receiving device 2000. The receiving device 2000 receives the signal from the transmitting device by a receiving antenna 2001, which is then output to a receiving processing unit 2002. The receiving processing unit 2002 downconverts the received signal to a baseband frequency band, performs an Analog to Digital (A/D) conversion, and removes CP in this order, and outputs the signal that has been processed to a reference signal separating unit 2003.
The reference signal separating unit 2003 separates the data signal and the reference signal multiplexed in the time domain, outputs the data signal to a DFT unit 2006, and outputs the reference signal to a propagation path estimating unit 2004.
The propagation path estimating unit 2004 estimates the propagation path between the transmitting and receiving devices using the received reference signal, and outputs the obtained propagation path estimation value to an equivalent propagation path calculating unit 2005.
For the propagation path estimation value input into the equivalent propagation path calculating unit 2005, the propagation path estimation value of the band corresponding to the clipping position is output to an equalization unit 2010 and a propagation path multiplying unit 2016 as a zero. As a result, this band is not actually used during transmission, an equivalent processing is performed when the signal transmitted without clipping processing travels over a poor propagation path, and the receiving power for the receiving device is zero.
The DFT unit 2006 converts the input data signal into a frequency domain signal via DFT. A demapping unit 2007 performs a decoding processing on the received signal to extract the signal from the transmitting device 1000 (FIG. 20). However, the spectra clipped in the transmitting device 1000 is viewed as having also been transmitted, and so zero data corresponding to the clipped amount is inserted into the extracted frequency signal by a zero insertion unit 2008.
A replica signal which will be described later is input into a cancel unit 2009 from the propagation path multiplying unit 2016. The cancel unit 2009 performs a subtraction of the replica signal from the received signal. The equalization unit 2010 performs an equalization processing using the output signal from the cancel unit 2009 and the propagation path estimation value from the equivalent propagation path calculating unit 2005. Afterwards, an IDFT unit 2011 performs a conversion to a time domain signal via IDFT. A demodulating unit 2012 conducts a demodulation processing on the output from the IDFT unit 2011, and outputs this to a decoding unit 2013. The decoding unit 2013 conducts an error correction decoding, and then outputs a soft estimation value to a replica generating unit 2014, in correspondence to an optional number of iterations of a non-linear equalization processing. When the iterative processing is to be completed, the soft estimation value of the information bit is output to a determining unit 2017, and the determining unit 2017 outputs a reception data D200 by performing a hard determination.
When the iterative processing continues, a soft replica is generated at the replica generating unit 2014, and after a DFT unit 2015 converts this to a frequency domain signal, the propagation path multiplying unit 2016 multiplies the propagation path estimation value to which the clipping value has been factored, and outputs this to the cancel unit 2009.
Thus, the reliability of the information bit obtained at the determining unit 2017 can be increased by iterative a cancel operation at the cancel unit 2009 for an optional number of iterations.